1. Technical Field
The present invention relates to a power amplifier circuit and a test apparatus. Particularly, the present invention relates to a power amplifier circuit which outputs an output voltage corresponding to an input voltage supplied thereto, and a test apparatus which tests a device under test.
2. Related Art
Conventionally, in testing a device under test such as a semiconductor circuit, etc., power source electricity for driving the device under test is supplied to the device under test. This power source electricity is generated by a power amplifier circuit.
The power amplifier circuit outputs a power source voltage corresponding to an input voltage supplied thereto, or outputs a power source current according to a current that has been consumed by the device under test. Conventionally, a push-pull circuit which includes two transistors functioning as power devices is used as the power amplifier circuit. A push-pull circuit is a circuit that adjusts the active nodes of the power devices to be at desired regions, by making an idling current flow through the power devices while outputting no power source current.
Presently, no related patent literature whatsoever has been identified, so indication of any literature is omitted.
The idling current of the power amplifier circuit changes according to the characteristics of the power devices. For example, even power amplifier circuits that have the same configuration might not have equivalent idling currents flow therethrough, due to any variations in the characteristics of the power devices thereof. Therefore, in some cases, the characteristics of the power amplifier circuit do not meet the design values. Further, in a case where a plurality of power amplifier circuits are used in parallel, the power amplifier circuits might show inconsistent characteristics.
Furthermore, the amount of the current flowing through the power devices changes as the temperature changes. Therefore, from when the power amplifier circuit is turned on till when the power amplifier circuit enters a static state, the idling current continues fluctuating and the characteristics of the power amplifier circuit also continue fluctuating.
Moreover, if such a power amplifier circuit is used in testing the device under test, a desired power source electricity might not be supplied to the device under test and a test of a high accuracy might not be conducted.
Though it is a conceivable option to insert a resistor having a high resistance at the output stage of the power amplifier circuit to reduce any influences caused by such variations, etc. in the characteristics of the power devices, this would degenerate the output impedance and also require a high voltage to be applied to the power devices in order for them to be driven, necessitating an increase in the power to be consumed by the power amplifier circuit.